Auroral Oval Research Articles

Formation and Motion of Horse Collar Aurora Events

AbstractThe polar cap can become teardrop shaped through the poleward expansion of the dusk and dawn sectors of the auroral oval, to form what is called horse collar aurora (HCA). The formation of HCA has been linked to dual‐lobe reconnection (DLR) where magnetic flux is closed at the dayside magnetopause. A prolonged period of northward IMF is required for the formation of HCA. HCA have previously been identified in UV images captured by the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instrument on‐board the Defense Meteorological Satellite Program (DMSP) spacecraft F16, F17 and F18. Events that have concurrent 630.0 nm all‐sky camera (ASC) data from the Redline Geospace Observatory (REGO) Resolute Bay site are now studied in more detail, making use of the higher cadence of the ASC images compared to DMSP/SSUSI. 11 HCA events are studied and classified based on the IMF conditions at the end of the event. Five of the events were found to end via a southward turning of the IMF, two end with positive By dominated IMF and four with negative By dominance. Under positive (negative) By the arcs move duskward (dawnward) in the northern hemisphere with the opposite true in the southern hemisphere. Under a southward turning the arcs move equatorward. One event is of particular interest as it occurred while there was a transpolar arc (TPA) also present. Understanding the evolution of HCA will allow DLR to be studied in more detail.

Study of time- and distance-dependent degradations of network RTK performance at high latitudes in Norway

In this study we examine the performance of a network real-time kinematic (NRTK) positioning service at high latitudes (approx 70^o N). The NRTK used is the Norwegian national positioning service “CPOS”. To test the performance, 6 geodetic quality receivers were deployed at various distances from the network receivers and used to collect positioning data for most of the year 2021. This test network is located in the night-time auroral oval region during normal conditions. Statistics are presented showing variation in performance as a function of the distance to the nearest NRTK receiver and as a function of the time-of-day. Performance is found to be significantly degraded during night-time, with approximately ten-fold increases of the occurrence of large positioning errors and significant increases in the time-to-fix. The distance from the network was also found to be a factor for significant performance degradation, with approximately ten-fold increases in the occurrence of large positioning errors when comparing results from a receiver close to the network (1.2 km) to a receiver a moderate distance away (11.5 km). The cause of the observed degradations are likely small-scale ionospheric density structures in the auroral oval region. Observational evidence of such gradients is shown.

Multi‐Event Conjugate Measurements of the SAR Arc Detachment From the Auroral Oval Using DMSP Satellites and an All‐Sky Camera at Athabasca, Canada

AbstractWe report the first statistical study of stable auroral red (SAR) arcs detached from the main auroral oval during non‐storm time, using multi‐event conjugate measurements by the Defense Meteorological Satellite Program (DMSP) satellites (F13–F19) and a ground‐based all‐sky imager at Athabasca (Canada) (54.6°W, 246.36°Е, MLAT = 61.5°, MLON = 308.3°, L = 4.4). We found 63 events of detached SAR arc conjunctions with the DMSP satellites in the northern hemisphere and 18 events in the opposite southern hemisphere from 2006 to 2018. Measurements aboard DMSP satellites show that detached SAR arcs are in general associated with enhancements of electron temperature (60 cases) and electron density troughs (58 cases). Only 14 cases show strong horizontal flow associated with the detached SAR arcs, indicating that the strong plasma flow is not a necessary condition to cause the detached SAR arcs. The electron temperature measured by DMSP associated with detached SAR arcs positively correlates with F10.7 solar activity index. The measured emission intensities at 630.0 nm in the SAR arcs show a good correlation with the electron temperature. These results indicate that the detached SAR arcs during non‐storm time are caused by heat flux from the magnetosphere associated with substorms, and their intensity depends on the background plasma condition in the ionosphere.

Formation of Electron Zebra Stripes Observed on 8 September 2017

AbstractZebra stripes are the characteristic structures having repeated hills and valleys in the electron flux intensities observed below L = 3. We delineate the fundamental properties and evolution of electron zebra stripes by modeling advection using time‐dependent electric fields provided by a global magnetohydrodynamics simulation. At the beginning of the simulation, the electrons were uniformly distributed in longitude. Some electrons moved inward due to enhanced westward electric field transients in the premidnight‐postdawn region. The inwardly displaced electrons were confined in a narrow longitudinal range and underwent grad‐B and curvature drifts. For any specific fixed position, the electrons periodically passed through the point with an energy dependent period, giving rise to the hills and valleys in the electron differential flux also known as zebra stripes. The valleys of the zebra stripes are composed of the electrons that underwent outward displacement, or no significant radial displacement. On the nightside, the duskside convection cell is skewed toward dawn in the equatorward of the auroral oval, and the westward electric field becomes dominant in the postdawn region, which results in the inward motion of the electrons. The spatial distribution of the westward electric field is consistent with observation. Zebra stripes are a mixture of the electrons that have and have not experienced inward transport due to solar wind‐inner magnetosphere coupling by way of the ionosphere.

Global Variations in the Time Delays Between Polar Ionospheric Heating and the Neutral Density Response

AbstractWe present results from a study of the time lags between changes in the energy flow into the polar regions and the response of the thermosphere to the heating. Measurements of the neutral density from the Challenging Mini‐satellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) missions are used, along with calculations of the total Poynting flux entering the poles. During two major geomagnetic storms in 2003, these data show increased densities are first seen on the dayside edge of the auroral ovals after a surge in the energy input. At lower latitudes, the densities reach their peak values on the dayside earlier than on the night side. A puzzling response seen in the CHAMP measurements during the November 2003 storm was that the density at a fixed location near the “Harang discontinuity” remained at unusually low levels during three sequential orbit passes, while elsewhere the density increased. The entire database of measurements from the CHAMP and GRACE missions were used to derive maps of the density time lags across the globe. The maps show a large gradient between short and long time delays between 60° and 30° geographic latitude. They confirm the findings from the two storm periods, that near the equator, the density on the dayside responds earlier than on the nightside. The time lags are longest near 18–20 hr local time. The time lag maps could be applied to improve the accuracy of empirical thermosphere models, and developers of numerical models may find these results useful for comparisons with their calculations.

Classification and Distribution of the Dayside Ion Upflows Associated with Auroral Particle Precipitation

Two important phenomena of the solar wind–magnetosphere–ionosphere coupling are auroral particle precipitation and the formation of ions flowing upward from the ionosphere. They have opposite transport directions of energy and substance. Based on the observations of particle precipitation and ion drift from the DMSP F13 satellite in January and July 2005, the ionospheric ion upflows in dayside auroral oval (0600–1800 MLT) can be divided into five types according to the velocity of ion upflows and the spectrum characteristics of auroral particle precipitation, and the distribution for different types of ion upflows is studied. The results show that the ion upflows mainly occur in the geomagnetic latitude (MLAT) range of 70–80°.The main magnetospheric source region of ion upflows (type A and D) caused by the accelerated electron (mainly the soft electron) corresponds to Low Latitude Boundary Layer (LLBL) and Cusp, and ion upflows of type B and C (related to the process of ambipolar diffusion caused by electron acceleration) mainly occur in LLBL and Boundary Plasma Sheet (BPS), while ion upflows of type E without electron acceleration mainly occur in the central plasma sheet (CPS).The dawn–dusk asymmetry is obvious in the winter season, with the ion upflows mainly occurring on the dawn/dusk side ionosphere. However, the ion upflows in summer mainly occur at the magnetic noon, with a symmetric distribution centered at the magnetic noon. The occurrence of ion upflow in winter is significantly higher than that in summer, and it is significantly enhanced during the period of moderate geomagnetic activity. The upward region expands to the lower latitude when the geomagnetic activity is enhanced. The effect of interplanetary magnetic field (IMF) components has also been studied in this paper. When IMF Bx is negative, the upflow occurrence increases in the region of 1500–1800 MLT and 0600–0900 MLT, with the MLAT range below 70°. The direction of IMF By may lead to the high-incidence area reverse at the prenoon or postnoon region. The occurrence of ion upflows with the MLAT range below 75° increases significantly when IMF is southward. Type A ion upflow has the highest velocity of ion upflows, followed by type E, and type D has the lowest. The average velocity of ion upflows in winter is significantly higher than that in summer.

Колебания геомагнитного поля в диапазоне 2.5–12 Гц в F-слое ионосферы по данным спутников SWARM

We have analyzed geomagnetic variations in the 2.5–12 Hz frequency range in the ionospheric F layer above the electron density maximum, using data from two SWARM satellites. The analysis is based on the data obtained under weak and moderate magnetic activity for 12 days in September and December 2016. To separate spatial inhomogeneities from time variations of the magnetic field, we analyzed signal waveforms and cross-spectra in a 2.56 s sliding window. A maximum in the occurrence and power spectral density of the variations was found at latitudes above the polar boundary of the auroral oval, which correspond to the magnetospheric input layers and dayside polar cusp/cleft. Typical waveforms of the high-latitude variations are the wave packets lasting for 5–10 periods, recorded with a short time delay by two satellites spaced by 40–100 km. These variations might be the ionospheric manifestation of the electromagnetic ion-cyclotron waves generated at the non-equatorial magnetosphere near the polar cusp. The waveforms and cross-spectra of the variations are examined in more details for two cases with different spatial distributions of the magnetic field in the ionosphere. For the ionospheric conditions corresponding to event 1 (September 17, 80° geomagnetic latitude, afternoon sector), spatial distributions of wave magnetic field in the ionosphere and on Earth are estimated using a model of Alfvén beam with a finite radius incident on the ionosphere [Fedorov et al., 2018].

Колебания геомагнитного поля в диапазоне 2.5–12 Гц в F-слое ионосферы по данным спутников SWARM

We have analyzed geomagnetic variations in the 2.5–12 Hz frequency range in the ionospheric F layer above the electron density maximum, using data from two SWARM satellites. The analysis is based on the data obtained under weak and moderate magnetic activity for 12 days in September and December 2016. To separate spatial inhomogeneities from time variations of the magnetic field, we analyzed signal waveforms and cross-spectra in a 2.56 s sliding window. A maximum in the occurrence and power spectral density of the variations was found at latitudes above the polar boundary of the auroral oval, which correspond to the magnetospheric input layers and dayside polar cusp/cleft. Typical waveforms of the high-latitude variations are the wave packets lasting for 5–10 periods, recorded with a short time delay by two satellites spaced by 40–100 km. These variations might be the ionospheric manifestation of the electromagnetic ion-cyclotron waves generated at the non-equatorial magnetosphere near the polar cusp. The waveforms and cross-spectra of the variations are examined in more details for two cases with different spatial distributions of the magnetic field in the ionosphere. For the ionospheric conditions corresponding to event 1 (September 17, 80° geomagnetic latitude, afternoon sector), spatial distributions of wave magnetic field in the ionosphere and on Earth are estimated using a model of Alfvén beam with a finite radius incident on the ionosphere [Fedorov et al., 2018].

Transient energetic particles as the origin of the mid-infrared north polar hotspot of Jupiter

Since it was detected in 1980, Jupiter's 8-μm CH4 north polar hot spot (8CNPHS), ∼20 K warmer than the surrounding polar stratosphere, has been observed for four decades. Unlike normal auroral ovals (i.e., the bright rings of auroral emissions), it is usually filled with bright emission. The causes of both its shape and longevity are not understood, although several mechanisms have been proposed to explain its existence. In order to investigate the deriving mechanism of the 8CNPHS, we have observed the north polar regions near 3 μm, where line emission from another CH4 band as well as a C2H6 fundamental band occur. Using Gemini North/GNIRS in 2013, 2020, 2021, and 2022, we have detected transient 3-μm CH4 and/or C2H6 bright spots within the 8CNPHS, and occasionally no apparent bright spots. By comparing the emission from CH4 with that from C2H6, we demonstrate that the origin of the 8CNPHS must be due to transient and energetic magnetospheric particles, which can penetrate down to the hydrocarbon layers, heating the homopause (∼1 μbar level) and the stratosphere (∼1 mbar level) and energize the 8CNPHS. Based on our observations and analysis, we propose the following three mechanisms for maintaining and containing the decades long warmth of the 8CNPHS: 1) energetic and transient auroral particle precipitations warming the stratosphere of the 8CNPHS, 2) a longer radiative cooling time in the 8CNPHS stratosphere (∼6 months) compared to less than or equal to one month at the homopause, and 3) recently detected polar stratospheric jets likely associated with polar fronts, which resist the free flow of warm gas in the 8CNPHS to the surrounding polar regions. We show that other heating mechanisms proposed so far in the literature, such as Joule heating, polar haze heated by sunlight, etc., are only the secondary mechanisms that follow atmospheric ionization caused by energetic particle bombardment. Our finding of the magnetospheric-ionospheric-stratospheric coupling in the Jovian polar regions open the possibility of quantitatively refining 3-D global circulation models for the atmospheres of giant planets and exoplanets.

SwarmFACE: A Python package for field-aligned currents exploration with Swarm

The SwarmFACE package utilizes magnetic field measurements by the Swarm satellites to study systems of field-aligned currents (FACs). Improvements of well-established techniques as well as novel single- and multi-satellite methods or satellite configurations are implemented to extend the characterization of FAC systems beyond the Swarm official Level-2 FAC product. Specifically, the included single-satellite algorithm allows to consider the FAC sheet inclination with respect to the satellite orbit and can work with low- or high-resolution data. For dual-satellite FAC estimation the package provides three algorithms, based on the least-squares, on the singular value decomposition, and on the Cartesian boundary-integral methods. These algorithms offer advantages over the corresponding Level-2 algorithm by providing more stable solutions for ‘extreme’ configurations, e.g. close to the orbital cross-point, and by allowing for a more general geometry of the spacecraft configuration. In addition, the singular value decomposition algorithm adapts itself to the spacecraft configuration, allowing for continuous, dual-satellite based FAC solutions over the entire polar region. Similarly, when Swarm forms a close configuration, the package offers the possibility to estimate the FAC density with a three-satellite method, obtaining additional information, associated to a different (larger) scale. All these algorithms are incorporating a robust framework for FAC error assessment. The SwarmFACE package further provides useful utilities to automatically estimate the auroral oval location or the intervals when Swarm forms a close configuration above the auroral oval. In addition, for each auroral oval crossing, a series of FAC quality indicators, related to the FAC methods’ underlying assumptions, can be estimated, like the current sheet inclination and planarity or the degree of current sheet stationarity.

Detecting the Auroral Oval through CSES-01 Electric Field Measurements in the Ionosphere

We present the results of a systematic study of the ionospheric electric field in the Auroral Oval (AO) region in the southern hemisphere. We exploit one year of electric field measurements taken by the Electric Field Detector (EFD) on board the Chinese Seismo-Electromagnetic Satellite-01 (CSES-01), flying at around 500 km altitude in a sun-synchronous orbit. We exploit the high temporal resolution of the EFD to devise a new technique for the detection of CSES-01 crossing of the AO using electric field measurements only. This new technique combines a Median-Weighted Local Variance Measure with Fast Iterative Filtering to automatically isolate high levels of electromagnetic activity caused by, e.g., particle precipitation and Field Aligned Currents (FACs) at auroral latitudes. We validate this new method against other standard proxies, such as the single-FAC product from the Swarm mission and the auroral radiance emission measured by the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) units on board the Defense Meteorological Satellite Program (DMSP) constellation. Furthermore, we identify ∼3000 orbits (out of a dataset of ∼10,000) where CSES-01 crosses the AO boundary under conditions of high geomagnetic activity. This dataset represents the first step in the systematic study of the auroral electric field, with many potential applications to space weather, thanks to the large amount of continuous observations of the ionosphere by CSES-01 and the forthcoming CSES-02 mission.

Substorms on a contracted auroral oval

The high-latitude magnetic substorms observed at geomagnetic latitudes higher 70° MLAT under the substorm absence at the lower latitudes are known as “substorms on the contracted oval” or “polar” substorms. Such substorms appear during quiet or weakly disturbed space weather conditions. The study of 254 “polar” substorms, recorded at the Scandinavian IMAGE magnetometer chain during the winter seasons of 2010–2020, confirmed a tendency to occur in the late evening (∼19–23 MLT), that is a bit earlier than the “normal” substorms (22–24 MLT). It was found that before the onset of “polar” substorms, like “normal” substorms, there is an increase in the PC-index indicating an energy input into the magnetosphere. We established that “polar” substorms, like “normal” substorms, are accompanied by positive mid-latitude magnetic bays, demonstrating a substorm current wedge (SCW) development.Several “polar” substorms are examined in detail. The ionospheric electrojets and field-aligned currents (FAC) distribution was studied basing on the AMPERE satellites measurements. We found that “polar” substorm onsets are associated with an enhancement of FACs in a localized evening area. Thus, “polar” substorms exhibited the properties, typical for “normal” substorms, so, they could be referred as a specific type of substorms developing under rather quiet space weather conditions.

Space environment and magnetospheric Poynting fluxes of the exoplanet τ Boötis b

Context. The first tentative detection of a magnetic field on the hot-Jupiter-type exoplanet τ Boötis b was recently reported by Turner et al. (A&A, 645, A59). The magnetic field was inferred from observations of circularly polarized radio emission obtained with the LOFAR telescopes. The observed radio emission is possibly a consequence of the interaction of the surrounding stellar wind with the planet's magnetic field. Aims. We aim to better understand the near space environment of τ Boötis b and to shed light on the structure and energetics of its near-field interaction with the stellar wind. We are particularly interested in understanding the magnetospheric energy fluxes powered by the star-planet interaction and in localizing the source region of possible auroral radio emission. Methods. We performed magnetohydrodynamic simulations of the space environment around τ Boötis b and its interaction with the stellar wind using the PLUTO code. We investigated the magnetospheric energy fluxes and effects of different magnetic field orientations in order to understand the physical processes that cause the energy fluxes that may lead to the observed radio emission given the magnetic field strength proposed in Turner et al. (A&A, 645, A59). Furthermore, we study the effect of various stellar wind properties, such as density and pressure, on magnetospheric energy fluxes given the uncertainty of extrasolar stellar wind predictions. Results. We find in our simulations that the interaction is most likely super-Alfvénic and that energy fluxes generated by the stellar wind-planet interaction are consistent with the observed radio powers. Magnetospheric Poynting fluxes are on the order of 1–8 × 1018 W for hypothetical open, semi-open, and closed magnetospheres. These Poynting fluxes are energetically consistent with the radio powers in Turner et al. (A&A, 645, A59) for a magnetospheric Poynting flux-to-radio efficiency >10−3 when the magnetic fields of the planet and star are aligned. In the case of lower efficiency factors, the magnetospheric radio emission scenario is, according to the parameter space modeled in this study, not powerful enough. A sub-Alfvénic interaction with decreased stellar wind density could channel Poynting fluxes on the order of 1018W toward the star. In the case of a magnetic polarity reversal of the host star from an aligned to anti-aligned field configuration, the expected radio powers in the magnetospheric emission scenario fall below the observable threshold. Furthermore, we constrain the possible structure of the auroral oval to a narrow band near the open-closed field line boundary. The strongest emission is likely to originate from the night side of the planet. More generally, we find that stellar wind variability in terms of density and pressure does significantly influence magnetospheric energy fluxes for close-in magnetized exoplanets.

Auroral oval reconstruction for historical geomagnetic storms in the 18th and 19th century

AbstractThe investigation of extreme space weather events can yield important information about the solar activity. Here, we present the reconstruction of the auroral oval position and size based on Bayesian inference for nine historical geomagnetic storms between 1716 and 1882, including the Carrington event in 1859, by using ground‐based observations, which enables us to derive the Kp index for historical events for the first time. The results for the latter show a very high level of geomagnetic disturbance (8.2 Kp 8.7, −929 nT Dst −1327 nT). Furthermore, we were able to derive the position of the pole in corrected geomagnetic coordinates, where especially the longitude is in good agreement with the position derived from the gufm1 model (Jackson et al., 2000). For the eight other historical storms, the Kp and Dst indices have been calculated here for the first time. In all cases, a very high Kp index was derived. The only exception is the geomagnetic storm from March 1716, which is, with a Kp index of , comparable with the St. Patrick's Day storm in 2015.

Dependence of Ionospheric Responses on Solar Wind Dynamic Pressure During Geomagnetic Storms Using Global Long‐Term GNSS‐TEC Data

AbstractTo elucidate the effect of solar wind dynamic pressure on the activities of ionospheric plasma irregularities in both high‐latitude and equatorial regions, we analyzed the long‐term global navigation satellite system (GNSS) total electron content (TEC) data from 2000 to 2018 and performed a superposed epoch analysis of the GNSS rate of the TEC index (ROTI), solar wind, interplanetary magnetic field (IMF), and geomagnetic index. We found that during the main phase of geomagnetic storms, the activities of ionospheric plasma irregularities were considerably enhanced in both high‐latitude and equatorial regions under high‐pressure conditions, and the equatorward edge of the auroral oval moved to lower latitudes. The poleward edge of the enhanced low‐latitude ROTI region (occurrence region of the plasma bubbles) in the evening sector extended to higher latitudes under high‐pressure conditions. During the recovery phase of geomagnetic storms, the plasma bubble occurrence in the dusk sector was suppressed under high‐pressure conditions. Our results suggest that the high‐latitude convection electric field and the penetration and disturbance dynamo electric fields at low latitudes become stronger during geomagnetic storms when the solar wind dynamic pressure is enhanced. This is because the conversion from solar wind energy to electromagnetic energy in the magnetosphere is enhanced by the formation of a high plasma pressure area in the high‐latitude cusp and mantle region. Therefore, not only the southward IMF but also solar wind dynamic pressure are important factors for varying global ionospheric responses during geomagnetic storms.

Quantifying the global solar wind-magnetosphere interaction with the Solar-Terrestrial Observer for the Response of the Magnetosphere (STORM) mission concept

Much of what we know about the solar wind’s interaction with the Earth’s magnetosphere has been gained from isolated in-situ measurements by single or multiple spacecraft. Based on their observations, we know that reconnection, whether on the dayside magnetopause or deep within the Earth’s magnetotail, controls the bulk flow of solar wind energy into and through the global system and that nightside activity provides the energized particles that power geomagnetic storms. But by their very nature these isolated in-situ measurements cannot provide an instantaneous global view of the entire system or its cross-scale dynamics. To fully quantify the dynamics of the coupled solar wind-magnetosphere requires comprehensive end-to-end global imaging of the key plasma structures that comprise the magnetosphere which have spatial resolutions that exceeds anything possible with multi-point or constellation situ measurements. Global, end-to-end, imaging provides the pathway to understanding the system as a whole, its constituent parts, and its cross-scale processes on a continuous basis, as needed to quantify the flow of solar wind energy through the global magnetospheric system. This paper describes how a comprehensively-instrumented single spacecraft in a high-altitude, high-inclination orbit coupled with ground-based instruments provides the essential observations needed to track and quantify the flow of solar wind energy through the magnetosphere. This includes observations of the solar wind plasma and magnetic field input, the magnetopause location in soft X-rays, the auroral oval in far ultraviolet, the ring current in energetic neutrals, the plasmasphere in extreme ultraviolet, the exosphere in Lyman-α, and the microstructure of the nightside auroral oval from ground-based all sky cameras.

Enhanced C2H2 Absorption Within Jupiter's Southern Auroral Oval From Juno UVS Observations

AbstractReflected sunlight observations from the Ultraviolet Spectrograph (UVS) on the Juno spacecraft were used to study the distribution of acetylene (C2H2) at Jupiter's south pole. We find that the shape of the C2H2 absorption feature varies significantly across the polar region, and this can be used to infer spatial variability in the C2H2 abundance. There is a localized region of enhanced C2H2 absorption which coincides with the location of Jupiter's southern polar aurora; the C2H2 abundance poleward of the auroral oval is a factor of 3 higher than adjacent quiescent, non‐auroral longitudes. This builds on previous infrared studies, which found enhanced C2H2 abundances within the northern auroral oval. This suggests that Jupiter's upper‐atmosphere chemistry is being strongly influenced by the influx of charged auroral particles and demonstrates the necessity of developing ion‐neutral photochemical models of Jupiter's polar regions.

An approach to detecting and eliminating spatial contour artifacts in Web GIS applications

One of the common problems of modern geoinformation libraries and interfaces when constructing spatial isolines is the presence of multiple artifacts in the resulting set, in particular, open level lines. As a result, the formed set of spatial isolines after the web rendering procedure makes it difficult to analyze the spatial distribution of the corresponding parameters, on the one hand, and reduces the quality of spatial image rendering, on the other. At the same time, artifacts of spatial isolines are especially critical for large amounts of data. The paper proposes an approach that makes it possible to correct software-generated isolines by identifying open lines and their subsequent selective connection. From the point of view of software implementation, the presented approach practically does not change the response time of server scripts. The effectiveness of the developed approach is confirmed by the example of a web application that provides visualization in the form of a set of spatial isolines of geophysical parameters in the auroral oval region.

Longitudinal variations in the position and magnitude of the poleward wall of the ionospheric trough in the southern hemisphere

For the first time, joint variations with longitude in the position of the high-latitude ionosphere structures: equatorward boundary of auroral diffuse precipitation, poleward wall and minimum of subauroral (main) ionization trough were considered. The data from the CHAMP satellite in the southern winter hemisphere in the evening, midnight and morning sectors were used, as well as a model of the auroral diffuse precipitation. The average (for all longitudes) distance between the equatorward boundary of the auroral oval and poleward wall increases from 1° in the evening to 2.5° in the morning, and between the auroral oval and trough minimum from 3.5° to 6.5°, respectively. These values agree well with the estimates obtained using different methods in other experiments. The poleward wall and minimum of the trough experience synchronous variations with longitude, the distance between the auroral oval and trough changes with longitude because of the different character of the longitudinal effect. Unexpectedly stable longitudinal variations in the magnitude of the poleward wall were identified for the first time: magnitude changes 4 times in the evening, 6 times at midnight and 3 times in the morning. Longitudinal variations in the poleward wall magnitude at midnight are completely correlated with the diffuse precipitation flux, in the evening with the electron density at mid-latitudes, and in the morning the poleward wall is clearly associated with electron density variations on the dayside. These results confirm the known assumptions that at midnight the poleward wall is completely formed by diffuse precipitation, and in the morning the poleward wall is evidently determined by the transport of ionization from the dayside. In the evening, the influence of residual solar ionization was probably manifested. In this sector, at America-Atlantic longitudes, an equatorward minimum of electron density is often formed, which prevents accurate determination of the trough position. These cases require a deeper analysis. In the evening at longitudes of America and at midnight at longitudes of 30°-90°, neither the poleward wall nor minimum of the trough is sometimes formed at all. This unexpected result requires clarification of the trough formation mechanism.

A unified model of cusp spot, High Latitude Dayside aurora (HiLDA)/(Space Hurricane), and 15MLT-PCA

Cusp spot, High Latitude Dayside aurora (HiLDA), ‘space hurricane’, and 15MLT-PCA (Polar Cap Arc observed around 15:00 Magnetic Local Time) are mesoscale auroral structures observed in the polar cap region. They share many common properties and, at the same time, have notable differences. A 15MLT-PCA is a polar cap arc connected to the auroral oval, but the others are auroral spots detached from the oval. A cusp spot differs from a HiLDA in local time location. A space hurricane differs from a HiLDA in having spiral-arm structures. Until now, relationships among these auroras have not been depicted clearly. Here we propose a unified model, based on lobe reconnection, that encompasses their similarities and differences. We then provide critical supporting evidence for the model. The model suggests that different reconnection sites under different IMF conditions result in these differently-appearing auroral forms. The model explains all the characteristic features of these auroras and has implications for understanding the dawn/dusk and inter-hemispheric asymmetries observed in their occurrence patterns. We anticipate confirmation of the model by observations to be made during the Solar wind-Magnetosphere-Ionosphere Link Explorer (SMILE) mission. Moreover, since the model indicates that these auroras appear on the footprint of the poleward cusp boundary, we expect data from the SMILE mission to make it possible to estimate the approximate shape of the cusp.